The present invention relates to a position detection apparatus for a motor, and more particularly, to a resolver phase calibration system and method for automatically calibrating an offset of a resolver in order to increase the precision of torque control and speed control of the motor.
Generally, a motor control unit (MCU) determines a coordinate system based on flux position to perform vector control of a synchronous motor or an induction motor, which may be used in an electric vehicle or in a hybrid electric vehicle. To make this determination, a resolver, which detects an absolute position of a rotor of the motor, is used.
The resolver is a type of a transformer, whereby if a shaft rotates while a voltage is applied to a primary coil (input side), the magnetic coupling coefficient changes, causing an output voltage having changed amplitudes for each carrier to be generated in a secondary coil (output side). The coils are arranged so that the output voltage will be changed to a sine wave and a cosine wave in response to a rotational speed of the shaft. Therefore, the rotating angle of the resolver can be determined by the ratio of amplitudes of the sine wave and the cosine wave.
The resolver is configured to detect a speed and a phase of the motor, and to provide corresponding position information to the MCU. The MCU uses the position information for torque and speed control of the motor. For these reasons, it is important to mount the resolver at a precise position. However, it is possible that error may occur during mounting of the resolver, as it is quite difficult to mount the resolver in a power train system. This error may make it impossible to detect a precise position and speed of the rotor of the motor, making it difficult to control the motor for optimal operation.
An example of a prior-art method to calibrate a sensing error of a resolver is a method that analyzes back electro-motive voltage signals between lines of the motor and waveforms of signals of the resolver, using measuring devices such as an oscilloscope, and then calibrates the errors. However, this method for calibrating sensing errors of a revolver is a manual process, requiring large amounts of time and effort. Furthermore, precise calibration cannot be guaranteed, so operation of the motor in an optimal operating range also cannot be guaranteed.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and should not be taken as an acknowledgement or any form of suggestion that this information forms prior art that is already known to a person skilled in the art.
In a preferred embodiment of the present invention, a resolver phase calibration system comprises a reference pulse generation unit, a resolver-to-digital converter (RDC), and a calibration phase calculating unit. The reference pulse generation unit is configured to generate a reference pulse signal based on a back electro-motive voltage signal of a motor. The RDC is configured to convert output signals of a resolver to a pulse signal, to count pulses of the converted pulse signal, and to output a digital output signal corresponding to the number of the pulses. The calibration phase calculating unit is configured to calculate a calibration phase of the resolver based on the reference pulse signal from the reference pulse generation unit and the digital output signal from the RDC.
It is preferable that the RDC comprises a first calculating member, a second calculating member, a third calculating member, a synchronization rectification unit, a voltage controlled oscillator, and a counter. The first calculating member is configured to multiply a sine wave signal output from the resolver by a cosine value of current position detection data. The second calculating member is configured to multiply a cosine wave signal output from the resolver by a sine value of the current position detection data. The third calculating member is configured to subtract an output signal of the second calculating member from an output signal of the first calculating member.
The synchronization rectification unit is configured to rectify an output signal of the third calculating member. The voltage controlled oscillator is configured to receive an output of the synchronization rectification unit, and to generate pulses having a frequency. Finally, the counter is configured to count the pulses generated by the voltage controlled oscillator and to generate the corresponding digital output signal.
Preferably, the reference pulse generation unit includes a comparator that compares the back electro-motive voltage signal with a reference voltage, and generates the reference pulse signal.
In another preferred embodiment of the present invention, the resolver phase calibration method comprises: generating a reference pulse signal based on a back electro-motive voltage signal of a motor; generating a digital output signal indicative of phase information of a resolver based on output signals of the resolver; calculating a resolver phase calibration value based at least in part on the reference pulse signal and the digital output signal; and calibrating a phase offset of the resolver based on the phase calibration value.
Preferably, the step of generating a digital output signal further comprises: multiplying a sine wave signal output from the resolver by a cosine value of current position detection data to generate a first product; multiplying a cosine wave signal output from the resolver by a sine value of the current position detection data to generate a second product; subtracting the second product from the first product to generate a resultant output signal; rectifying the resultant output signal to generate a rectified output signal; generating pulses having a frequency related at least in part to the rectified output signal; and counting the generated pulses and generating the corresponding digital output signal.
In yet another preferred embodiment of the present invention, a resolver phase calibration system comprises a reference pulse generation unit, a resolver-to-digital converter (RDC), and a calibration phase calculating unit. The reference pulse generation unit generates a reference pulse. The RDC converts output signals of a resolver to a digital output value representing a phase difference related to the resolver position. The calibration phase calculating unit calculates a calibration phase of the resolver based at least in part on the reference pulse signal from the reference pulse generation unit and the digital output signal from the RDC.